An air suspension utilizing air pressure is often used, particularly in vehicles, to realize high grade control in concatenation with electronic control devices because the suspension characteristic may be easily changed.
An example of the constitution and operation of a circuit for adjusting body height by air suspension is disclosed in the examined published Japanese patent No. 28589/1975. This circuit also provides high pressure and low pressure tanks in addition to a compressor as an air pressure source, supplies air to the air chamber of each air suspension of each wheel from a high pressure tank and returns the air exhausted from the air suspension to the low pressure tank. Since the compressor compresses the air in the low pressure tank to supply the air to the high pressure tank, operating energy usage of the system as a whole can be reduced.
However, such energy reduction effect of compressor is not yet sufficient in a reciprocal piston type compressor. Namely, a compressor of this type is provided with a suction port and an exhaust port, each having a valve to the one cylinder piston chamber; and load and energy loss result during compression because the other cylinder chamber is generally in communication with atmospheric air, resulting in a large pressure difference between the two sides of the piston.